On using CAV and OBE in seismic monitoring of nuclear power plant

Posted on Sep 24, 2014 in News

Operating basis earthquake ground motion (OBE) is the ground motion for which those features of the NPP necessary for continued operation without undue risk to the health and safety of the public will remain functional (NRC Regulations, Appendix S to Part 50—Earthquake Engineering Criteria for Nuclear Power Plants). The operating basis earthquake ground motion is only associated with plant shutdown and inspection unless specifically selected by the applicant as a design input. Parameters of the OBE are estimated on the basis of integrated geologic, geophysical, and geotechnical investigations.

The USNRC (U.S. Nuclear Regulatory Commission 1997) uses standardized CAV (cumulative absolute velocity) as one of the ground motion measures to determine whether a nuclear power plant must be shut down after an earthquake when the OBE ground motion is exceeded. Standardized CAV (EPRI 2006) is used in conjunction with response-spectral acceleration and velocity, and is a measure of a potential damage. CAV is calculated from the acceleration time history using integral formula by means of the standardized procedure (EPRI 2006).

For OBE exceedance to occur, the recommended criterion requires exceedance of both a response spectrum parameter and a damage parameter, referred to as CAV.

Weir-Jones, and our manufacturing arm Terrascience, has been maturing with the nuclear industry for many years. We have many of our analog seismic monitoring systems out, all over the world, and they run as well today, as they did when they were installed. we have, of course, grown with the industry as well, and this is shown in the evolution of our equipment for analog beginnings to pure digital accelerometers, recorders and software.

The above note outlines the criteria we have deployed in our acquisition software, AUTOTAR, to accommodate the required CAV measurements that all operating nuclear power plants (NPP) rely on for continued safe operation. We are very excited to see our clients update their analog systems to full on digital systems with our new software packages. Most exciting indeed!


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